Generally, a boiler is installed in a variety of buildings including homes, offices, factories and the like, and supplies hot water and heating water through a heat exchange between water and a heat source generated by burning a mixture of air and a gas.
For this purpose, the boiler includes a fuel supplier which receives each of air and a gas from an outside and mixes the air with the gas to supply a mixed fuel to a burner, the burner receives the mixed fuel from the fuel supplier and generates a flame by burning the mixed fuel, and a heat exchanger which exchanges heat between circulating heating water and a heat source supplied from the burner to heat the circulating heating water as heating water.
Recently, a condensing heat exchanger, which is provided with a sensible heat exchanger primarily exchanging heat between circulating heating water and sensible heat generated at a burner and a latent-heat exchanger secondarily exchanging heat between the circulating heating water and combustion gas undergoing heat exchange in the sensible heat exchanger, is widely used, and a boiler provided with such a condensing heat exchanger is referred to as a condensing boiler.
Also, a boiler for heating and hot water being used in a home may be classified into an oil boiler and a gas boiler according to fuel that is used, and of those the gas boiler which is convenient to use and generates less air pollution is mainly used.
FIG. 1 is a diagram illustrating a downstream type condensing gas boiler among conventional condensing gas boilers. As shown in FIG. 1, the conventional condensing gas boiler is configured with an expansion tank 3 in which a circulating heating water inflow pipe 1 and a circulating heating water discharge pipe 2 are connected to a lower part portion thereof and storing circulating heating water that flows in through a circulating heating water inflow pipe 1, a circulating pump 4 circulating the circulating heating water discharged through the circulating heating water discharge pipe 2 connected to the expansion tank 3, a latent-heat exchanger 5 in which the circulating heating water, which is pumped by the circulating pump 4, exchanges heat with latent heat, which is generated when condensed water is created due to a temperature decrease of combustion gas while passing through a heat exchange pipe 5a installed at the latent-heat exchanger 5, a sensible-heat exchanger 6 transferring heat energy of a burner 7 to the circulating heating water that is primarily preheated through the latent-heat exchanger 5, a three way valve 10 supplying the heating water to a heating water supply pipe 8 when a heating operation is performed and to a hot water heat exchanger 9 when a hot water supplying operation is performed, and the hot water heat exchanger 9 heating direct water to supply hot water to a user when the hot water supplying operation is performed.
By looking at an operation process of the conventional condensing gas boiler shown in FIG. 1, circulating heating water losing heat to a heating required zone flows in the expansion tank 3 by passing through the circulating heating water inflow pipe 1, and the circulating heating water, which passes through the expansion tank 3 to be discharged to the circulating heating water discharge pipe 2, is supplied to the latent-heat exchanger 5 via the circulating pump 4, exchanges heat with latent heat, which is generated when condensed water is created due to a temperature decrease of combustion gas while passing a heat exchange pipe 5a installed at the latent-heat exchanger 5, and primarily rises in temperature.
Also, the circulating heating water rising in temperature at the latent-heat exchanger 5 secondarily exchanges heat with the combustion gas through the sensible-heat exchanger 6 to rise in temperature. At this point, the condensed water being created is discharged to the outside through a condensed water drain path 13.
Meanwhile, the circulating heating water being secondarily heated at the sensible heat exchanger 6 is supplied to a heating required zone through a heating water supply pipe 8. At this point, the three way valve 10 is provided at the heating water supply pipe 8 and the heating water is supplied to the hot water heat exchanger 9 through the three way valve 10 to heat direct water flowing in through a direct-water inflow pipe 11 into hot water, and then the hot water is discharged through a hot water outlet pipe 12 or is supplied to the heating required zone to provide heat thereto.
However, the conventional condensing gas boiler configured as described above heats direct water into hot water only using heating water such that there are problems in that a long time is necessary to heat the direct water and also an excessive amount of heat is consumed to heat the direct water into the hot water.
Also, a cross section of the heat exchange pipe 5a, which is connected to the circulating heating water discharge pipe 2 so that the circulating heating water undergoes a heat exchange while moving therethrough, has a circular shape such that there is a problem in that a heat transfer area at which heat is exchanged between the circulating heating water and latent heat is small and thus heat transfer efficiency is dramatically degraded.
In addition, even though a plurality of heat exchange pipes 5a are configured to increase a heat transfer area, there is a problem in that an increase of the number of the heat exchange pipe 5a is restricted due to a limitation of a dimension of the latent-heat exchanger.